1. Field of the Invention
The present invention relates to a paper dehumidifying unit to be placed in a paper feeding device of an apparatus such as an electrophotographic copy machine. More particularly, the present invention relates to a paper dehumidifying unit for an image forming apparatus including heating means which is disposed between a plurality of paper feeding trays being placed in the paper feeding device or under the tray and performing the dehumidification of the copying paper under a convection current of heat in the paper feeding device by causing the heat emanated from the heating means not to be directly transmitted to copying paper.
2. Description of the Related Art
An image forming apparatus such as an electrophotographic copy machine includes a plurality of paper feeding trays disposed in the lower part of the body of the apparatus to make up a paper feeding device from which sheets of copying paper of any size can be fed out of those different in size and accommodated in the paper feeding trays installed therein. When the toner image formed on an image carrier such as a photosensitive drum is transferred onto copying paper in the image forming apparatus, the humidity contained in such copying paper has been known to greatly affect the transfer operation. When the moisture content of copying paper is high, for example, the transfer of such a toner image is not carried out in good condition and the problem is that copy quality is deteriorated as whites are generated in the image. When the moisture content of copying paper is locally high, moreover, the copying paper tends to wave and when it is heated while being passed through a fixing apparatus, the wavy condition of the copying paper lets such problems arise as making the copy look unattractive, causing jamming when it is conveyed through the paper conveying channel, inferior image transfer and so forth.
In order to solve the aforesaid problem attributed to the moisture content of copying paper, heating means are arranged for paper feeding trays or the like to regulate the humidity of copying paper. Unexamined Japanese Patent Publication No. Sho. 56-72452, for example, discloses an arrangement in which a heating means is provided at the rear end of paper feeding tray in the paper feeding direction so as to dehumidify not only copying paper thereby but also the interior of an image forming apparatus by circulating hot air therein. Moreover, Unexamined Japanese Utility Model Publication No. Sho. 56-102552 and Unexamined Japanese Patent Publication No. Sho. 61-69627 also disclose an arrangement, for example, in which heating means are placed above a paper feeding tray where copying paper is accommodated to exert heating action onto upper sheets of copying paper in the tray. When heating means are arranged above the tray, the copying paper fed by paper feed rollers or the like is dehumidified efficiently.
However, the heat emanating from the heating means is directly applied to copying paper when a dehumidifying unit of the sort mentioned in the above related art is employed and the side portion of copying paper containing much moisture is caused to wave in conspicuous curves accordingly. Therefore, there arises the problem of not solely hindering copying paper from being conveyed because of its wavy condition as noted previously but also causing trouble to the transfer of a toner image. When the moisture contained in copying paper is distributed unevenly, copying paper becomes rugged when it is directly heated and this also poses a problem in that good copying quality is not maintained because it is not allowed to contact the photosensitive drum uniformly.